Department of Cell and Molecular Physiology, University of North Carolina Neuroscience Center, University of North Carolina School of Medicine, Chapel Hill, NC 27599-7545, USA.
J Neurosci. 2010 Apr 21;30(16):5653-67. doi: 10.1523/JNEUROSCI.6187-09.2010.
Slit/Roundabout (Robo) signaling controls midline repulsive axon guidance. However, proteins that interact with Slit/Robo at the cell surface remain largely uncharacterized. Here, we report that the Drosophila transmembrane septate junction-specific protein Neurexin IV (Nrx IV) functions in midline repulsive axon guidance. Nrx IV is expressed in the neurons of the developing ventral nerve cord, and nrx IV mutants show crossing and circling of ipsilateral axons and fused commissures. Interestingly, the axon guidance defects observed in nrx IV mutants seem independent of its other binding partners, such as Contactin and Neuroglian and the midline glia protein Wrapper, which interacts in trans with Nrx IV. nrx IV mutants show diffuse Robo localization, and dose-dependent genetic interactions between nrx IV/robo and nrx IV/slit indicate that they function in a common pathway. In vivo biochemical studies reveal that Nrx IV associates with Robo, Slit, and Syndecan, and interactions between Robo and Slit, or Nrx IV and Slit, are affected in nrx IV and robo mutants, respectively. Coexpression of Nrx IV and Robo in mammalian cells confirms that these proteins retain the ability to interact in a heterologous system. Furthermore, we demonstrate that the extracellular region of Nrx IV is sufficient to rescue Robo localization and axon guidance phenotypes in nrx IV mutants. Together, our studies establish that Nrx IV is essential for proper Robo localization and identify Nrx IV as a novel interacting partner of the Slit/Robo signaling pathway.
Slit/Roundabout（Robo）信号通路控制着中线排斥性轴突导向。然而，与 Slit/Robo 在细胞表面相互作用的蛋白质在很大程度上仍未被描述。在这里，我们报告了果蝇跨膜分隔连接特异性蛋白 Neurexin IV（Nrx IV）在中线排斥性轴突导向中的作用。Nrx IV 在发育中的腹神经索神经元中表达，并且 nrx IV 突变体显示同侧轴突的交叉和盘旋以及融合的连合。有趣的是，在 nrx IV 突变体中观察到的轴突导向缺陷似乎与其其他结合伴侣（如 Contactin 和 Neuroglian 以及与 Nrx IV 反式相互作用的中线胶质蛋白 Wrapper）无关。nrx IV 突变体显示 Robo 定位弥散，并且 nrx IV/robo 和 nrx IV/slit 之间的剂量依赖性遗传相互作用表明它们在共同的途径中起作用。体内生化研究表明 Nrx IV 与 Robo、Slit 和 Syndecan 相关，并且 Robo 和 Slit 之间的相互作用，或 Nrx IV 和 Slit 之间的相互作用，分别在 nrx IV 和 robo 突变体中受到影响。在哺乳动物细胞中共表达 Nrx IV 和 Robo 证实了这些蛋白质在异源系统中保留相互作用的能力。此外，我们证明了 Nrx IV 的细胞外区域足以挽救 nrx IV 突变体中的 Robo 定位和轴突导向表型。总之，我们的研究确立了 Nrx IV 对于 Robo 正确定位是必不可少的，并确定 Nrx IV 是 Slit/Robo 信号通路的一个新的相互作用伙伴。
